Heat-sensitive copying paper



y 1959 M. VAN DAM 2,897,090

HEAFSENSITIVE COPYING PAPER Filed April 11, 1957 v SOURCE OF RADIANTENERGY \LlGHT-TRANSMITTING BASE HEAT-SENSITIVE COATING HEAT- SENSITIVECOPY MEDIUM FIG. 2.

I BASE ORIGINAL TO BE COPIED\ HEAT-SENSITIVE COATIN INVENTOR MAX VAN DAMLIGHT-TRANSMITTING BY ATTONEY HEAT-SENSITIVE COPYING PAPER Max Van Dam,Newton, NJ., assignor to Anken Chemical & Film Corporation, Newton, NJ.

' Application April 11, 1957, Serial No. 652,103

12 Claims. (Cl. 117-36) This invention relates to an improvedheat-sensitive duplicating paper useful in preparing copies of printedmatter or the like.

More specifically, this invention is concerned with heat-sensitivecoating and coated sheet materials designed for preparing copies ofprinted matter or other graphic subject matter by exposure to highintensity irradiation and without subsequent developing or fixingoperations.

Heat-sensitive coatings of this type, for preparing copies by directexposure to high intensity irradiation without further treatment, areknown, and several have been described, as in Miller and Clark, US.Patents 2,663,654, issued December 22, 1953, and 2,710,263, issued June7, 1955; also Miller, US. Patent 2,740,896, issued April 3, 1956.

Significant limitations or disadvantages exist in the coatings for thispurpose heretofore described however. Perhaps the most important ofthese is the lack of black and white contrast in copies made with thesecoatings. In most instances, the white is not white and the black notblack. Frequently, the copying paper shows a butt background rather thanwhite; and by virtue of the components used, a violet or blue imageresults instead of a neutral black. While heat-sensitive coatings with awhite background are known, these produce an image which is most oftendark brownish rather than black. True black and white copies have notbeen achieved.

Lack of sharp outline in black and white copies is also encountered inthese previously described coatings. The boundary between the lightbackground and the image is insufiiciently distinct in the copiesresulting from them; a spreading or bleeding effect occurs; the copiedimage thus is unsharp or blurred.

Another major limitation of prior coatings is the narrow range ofexposure conditions which will produce a satisfactory readable copy.Exposure to the optimum quantity of radiant energy may give reasonablyacceptable results; but minor variations in the amount of irradiationgive poor or unreadable copies. Underexpo sure to a relatively smalldegree produces too light a copy with insufficient contrast;overexposure to the same extent produces a copy with too dark abackground.

A still further drawback to previously proposed coatings is that theircomponents are so reactive and unstable toward each other that they mustbe ground or mixed separately, and in many instances, even applied tothe sheet material as separate multiple coatings.

Still another drawback is the sensitivity of prior coatings toimpurities such as small particles of chemical mat'erials and coarsedust. Such impurities show up as dark spots on the copy.

It is, therefore, an object of my invention to provide novel and usefulcompositions as coatings for copying paper which can produce neutralblack and white copies.

Another objectof my invention is to provide compositionsrof aheat-sensitive material which will produce 2,897,090 Patented July 28,1959 varied quantities of radiant energy.

Another object of my invention is to provide compositions of aheat-sensitive coating which will afiord copies sharp and clear, withditsinct boundaries between the image and the background.

Still another object of my invention is to provide compositions whichcan be ground and mixed in one operation, and applied to the sheetmaterial as a single coating.

A further object is the provision of heat-sensitive copying paper whichis not oversensitive to impurities.

In conventional photography, the black image and the gray tones consistof metallic silver, reduced to the metal state from silver salts by theaction of light and, of course, a suitable developer. The presentinvention is based on the discovery that under certain conditions blackand neutral gray tones can be formed of metallic bismuth, suitablyreduced to the metal state from bismuth salts. The requisite conditionsare similar to those for the well-known reaction in aqueous alkalinesolution whereby a bismuth salt can be reduced by sodium stannite tometallic bismuth.

In place of sodium stannite or other tin salt and an alkali hydroxide,which are unstable and impractical (sodium stannite forms stannate inair, and the hydroxide changes into carbonate), this invention makesprimary use of derivatives of tin and organic alkaline compounds.

Bismuth is the key ingredient in this process, as silver is the keyingredient in photographic processes. The starting point is a bismuthsalt and the process reduces it to metallic bismuth. Reduction takesplace only in the presence of heat.

The required ingredients for a coating composition made in accordancewith this invention are the follow- (l) A bismuth salt.

(2) A reducing agent. (3) A suitable medium. (4) A reaction regulator.(5) A binder (optional).

organic reducing agents may also be used, such as so-' diumhydrosulfite. Suitable organic tin derivatives are piperidine-tinchloride, semicarbaZide-tin sulfate, diphenylamine-tin chloride,methylamine-tin sulfate, aniline-tin sulfate, tin oxalate, tin tartrate,tin citrate, tin glycolate, and tin formate. These organic tinderivatives are illustrative of the various derivatives of this naturewhich have beenmade from semicarbazide, hydrazine, pyridine, aniline,methylamine, trie'thylarnine, triethanolamine, triisopropanolamine,piperidine, di phenylamine.

(3) A suitable medium: An alkaline medium, preferably organic, ispreferred and suitable compounds are: semicarbazide, heterocyclic baseand their derivatives such as amino-pyridine amines and aminoderivatives, e.g. ethanolamines. Liquid alkaline substances can be used,preferably by converting them into new solid compounds through additionor condensation with weakly acid-reacting compounds. As liquid compoundsmay be used: Methylamine, dimethylamine, aniline, pyridine,

3 quinoline, hydrazine, triethylamine, triethanolamine, piperidine. Theymay be combined with: Ox-alic acid, tartaric acid, salicylic acid,benzoic acid.

.(4) Reaction'regulator: Regulators may be used to control the spread ofthe reaction and hence the sensitiyity or range of the coating todifierent amounts of radiant energy. As regulators, low-meltingmaterials are used, preferably but not necessarily organic alkalinecompounds. Suitable compounds for this purpose have been found to bebenzylthiocyanate, chlorophenol, cinnamyl alcohol, o-cresol,diphenylamine, hexadecanol, exad y m p-t luidine, riph nyl P o p -vanilin, amino diphenylamine, p-hydroxy diphenylamine and phenyldiethanolamine. The dry ingredients of the mixture do not react quicklyand these last listed materials are used to lower the melting point.

(5) Binder: A suitable binder in solution, and coating modifiers such asplasticizers, softeners, etc., may be used, Typical binders suitable forthe purposes of this invention are the following: cellulose acetate,cellulose acetobutyrate, cellulose nitrate, ethyl cellulose, rubber nd hna ub e and hyl hvr roxy thyl lulose.

As has above been indicated, the key element in the entire process isbismuth but since we start with-a bismuth compound, it is necessary toutilize a reducing agent. Since the reaction will take place best in asuitable medium, the medium is also provided. Nonetheless, since thereaction may also take place without such medium, the latter is employedsolely to expedite and facilitate the reaction. By the same token, aregulator is also used to control the reaction in order to providesharply defined results but in the absence offsuch regulater, thereaction would still take place and with good results, fallingshort,-however, of the excellent results attained with the use of aregulator. The use of a binder is not essential and when used a smallamount suflices. The binder helps to prevent setting of the materialsduring the coating process and keeps them in suspension. It alsoprovides better adhesion to the paper.

It will be apparent from the foregoing, that the two key ingredients ofthe present invention are a bismuth compound and a reducing agent. Butthe other three ingredients are used to improve the process and forimproved results. Aside from the fact that these three ingredients arenot absolutely essential in the reaction, there may also be overlappingwhich would reduce their number without loss of their respectivefunctions. For example, the alkaline medium and the regulator mayoverlap in that the regulator is preferably an organic alkalinecompound. Consequently, it would not only perform the function ofcontrolling the reaction but it would also supply the alkaline medium inwhich the reaction would take place.

Compositions prepared in accordance with this invention may be appliedas a coating to paper, film and other light-transmitting material,either transparent or translucent, and other sheet materials may be usedproviding that they are transparent to heat. The result is aheatsensitive copy-medium. The invention is illustrated in theaccompanying drawing, in which:

Fig. 1 shows the manner of use of a heat-sensitive copy-medium made inaccordance with this invention, sald copy-medium and the original to becopied being shown in section and the radiations from the heat sourcebemg represented by means of interrupted lines.

Fig. 2 1s a plan View of said heat-sensitive copymediurn superimposedupon the original to be copied, said v ew following the exposure of saidcopy-medium and said original to radiant energy, one corner of saidcopy-medium being folded over to show the result of such exposure.

Referring now to Fig, 1 of the drawing, it will be observed that in theuse of a heatfsensitive copysmedium 1n accordance with this invention,said copy-medium is superimposed upon and in contact with the originalwhich is to be copied. In the drawing, the heat-sensitive copy-medium isshown to consist of a light-transmitting I base, such as a sheet oflight-transmitting paper, covered with a heat-sensitive coating preparedin accordance with this invention.

The heat-sensitive copy-medium is superimposed upon and in contact withthe original to be copied, said original being shown in the drawing as asheet of paper or the like having printed, typewritten or writtenmaterial applied thereto and indicated by the interrupted lines thereon.

Radiant energy is then applied through said heat-sensitive copy-mediumto the original to be copied. This is done by the use of any suitablesource of radiant energy, as for example an infra-red lamp as shown inFig. l of the drawing. The interrupted lines between said infrared lampand said heat-sensitive copy-medium are intended to represent theradiations which emanate from said infra-red lamp.

More heat is generated by said radiant energy in the printed or otherwritten matter on the original to be copied than in the blank spacessurrounding said printed or written matter, such heat being .suflicientto cause the chemical reaction in the heat-sensitive coating hereindescribed. The bismuth compound is reduced .to metallic bismuth in theprecise areas on the heat-sensitive copymedium which correspond to thegraphic material on the original to be copied, and the result is that anidentical copy of said graphic material is formed on the heatsensitivecopy-medium and indicated in the drawing by the interrupted lines on theheat-sensitive Opyrmedium shown in Fig. 2.

The following coating compositions are given as specific examplesillustrative of the invention and they are. not to be consideredrestrictive or limitative of its scope:

After mixing, the mixture was uniformly spread bymeans of a doctor-bladeonto a thin transparent paper and dried at room temperature.

The resulting sheet is suitable for use as a heat-sensitive copyingpaper.

The following mixture was ball milled and coated on light transmittingpaper;

h following mi ture s ba -milled and sea e 1. light transmitting paper:

G am Bismuth subsalicylate 36 Tin hydroxide v 20 Tri-isopropanolamine 19Polyvinylbutyral V 25 Semicarbazide 2-5 Toluene a 30 The followingmixture was ball-milled and coated on translucent paper:

Bismuth lactate g 36 Semicarbazide-tin chloride ..g 34 Semicarbazide g15 Hydrazine salicylate g 20 Ethyl hydroxyethyl cellulose g.. 1 Toluene7 l 50 Ligroine ml. 400

The following mixture was ball-milled and coated on transparent paper:

Grams Bismuth subnitrate 2930 Triethylamine-tin chloride 2910Semicarbazide 2500 Ethyl paratoluene sulfonate 1000 Cellulose nitrate200 Acetone 2300 It will be noted that organic tin derivatives are usedin the foregoing examples. The following procedures may be used inproducing these derivatives:

A. Preparation of piperia'ine-tin chloride To a solution of 190 g. ofanhydrous tin chloride in 500 ml. of water was added 85 g. ofpiperidine.

The white precipitate which formed was immediately filtered olf, washedwith water, methanol and dried.

Yield: 81 g. of piperidine-tin chloride.

B. Preparation of semicarbazide-tin sulfate 150 g. of semicarbazidedissolved in 230 ml. of water was added to a solution of 215 g. ofanhydrous tin sulfate in 230 ml. of water.

The mixture warmed spontaneously and precip tate was formed. Afterstanding for 2 hours the precipitate was filtered 'ofi, washed withwater, then with methanol and dried. I

Yield: g. of semicarbazide-tin sulfate in the form of a white powder.

C. Preparation of diphenylamine-tin chloride A solution of 338 g. ofdiphenylamine in 50 ml. of methanol was added to a solution of 190 g. ofanhydrous tin chloride in 500 ml. of water; immediately a precipitatewas formed. One liter of methanol was added to the slurry. Theprecipitate was filtered, washed with water and methanol.

Yield: 500 g. of diphenylamine-tin chloride in the form of a white.powder. 7

D. Preparation of methylamine-tin sulfate To a solution of 215 g. ofanhydrous tin sulfate in 500 ml. of water was added 120 g. of a 25%solution of methylamine in water. The white precipitation which formedwas immediately filtered oif, washed with water, then with methanol anddried.

Yield: 60 g. of methylamine-tin sulfate in the form of a white powder.

E. Preparation of aniline-tin sulfate To a solution of 107 g. ofanhydrous tin sulfate in 250 F. Preparation of hydrazine tarzrate To asolution of 1 50 g. of tartaric acid in 500 ml. of

methanol was added 50 g. of hydrazine monohydrate.

The white precipitate which was formed immediately,

was filtered, washed with methanol and dried.

Yield: g. of hydrazine tartrate.

G. Preparation of hydrazine salicylate To a slurry of 151 g. ofsalicylic acid in 200 m1. of .methanol was added: 67 g. of hydrazinemonohydrate.

The mixture warmed spontaneously and the salicylic acid.

went into solution. The methanol was evaporated on a steambath. Aftercooling the residue solidified:

Yield: g. of hydrazine salicylate.

The foregoing is illustrative of the basic principles of this inventionand it will be understood that all of the examples above set forth aremerely illustrative of the invention and not limitative thereof and thatmodifications and variations of these examples, as well as otherexamples involving other procedures and formulae producing the same orsimilar results may also be employed within the broad spirit of theinvention and the broad scope of the claims.

I claim:

1. A heat-sensitive copying sheet for producing copies of printed orgraphic subject matter by exposure of said sheet, in contact with saidsubject matter, to radiant energy, said copying sheet having appliedthereto the combination of a bismuth compound and a tin derivativereducing agent capable of reacting with said bismuth compound in thepresence of heat to produce metallic bismuth.

2. A heat-sensitive copying sheet for producing copies of printed orgraphic subject matter by exposure of said sheet, in contact with saidsubject matter, to radiant energy, said copying sheet having appliedthereto the combination of a bismuth compound and a reducing agentcapable of reacting with said bismuth compound in the presence of heatto produce metallic bismuth, said bismuth compound being a bismuth saltwhich is combined with a tin derivative reducing agent in an organicalkaline medium.

3. A heat-sensitive copying sheet for producing copies of printed orgraphic subject matter by exposure of said sheet, in contact with saidsubject matter, to radiant energy, said copying sheet having appliedthereto the combination of a bismuth compound and -a reducing agentcapable of reacting with said bismuth compound in the presence of heatto produce metallic bismuth, said bismuth compound being a bismuth saltwhich is 'combined with a tin derivative reducing agent in an alkalinemedium and held together by a binder.

4. A heat-sensitive copying sheet for producing copies of printed orgraphic subject matter by exposure of said sheet, in contact with saidsubject matter, to radiant energy, said copying sheet having appliedthereto the combination of a bismuth compound and a reducing agentcapable of reacting with said bismuth compound in the presence of heatto produce metallic bismuth, said bismuth compound being a bismuth saltselected from the group consisting of the bismuth salts of inorganic andorganic acids and being combined with a reducing agent selected from thegroup consisting of inorganic and organic tin derivatives.

5. A heat-sensitive copying sheet for producing copies of printed orgraphic subject matter by exposure of said sheet, in contact with saidsubject matter, to radiant energy, said copying sheet having appliedthereto the combination of a bismuth compound and a reducing agentcapable of reacting with said bismuth compound in the presrubber andethyl hydroxyethyl cellulose.

6. A heat-sensitive copyingsheet for producing copies of printed orgraphic subject matter by exposure of said sheet, in contact with saidsubject matter, to radiant energy, said copying sheet having appliedthereto the combinationof abismuth compound and-a reducing agent capableof reacting with said bismuth compound in the presence of heat :toproduce metallic bismuth, the hismuth compound being a bismuth saltwhich is combined with a tin derivative reducing agent and a reactionregulator'in an alkaline medium and ;-held togetherzby a binder, saidreaction regulator being a low melting material selected from the @groupconsisting of henzylthiocyanate, chlorophenol, cinnamyl alcohol,-o-cresol, diphenylarnine, hexadecanol, hexade'cylamine, .p-toluidine,triphenyl phosphate, o-vanillin, .arnino diethanolamine.

7. A heat-sensitive copying sheet for producing copies of printedorgraphic subject matter by exposure of said sheet, in contact with saidsubject matter, to radiant energy, said copying sheet having appliedthereto the combination of a bismuth compound and a reducing agentcapable of reacting with said bismuth compound in the presence of heatto produce metallic bismuth, said bismuth compound consisting ofapproximately 2690 parts by weight of bismuth borate, which 'is combinedwith the following ingredients in the following approximate parts byweight for applying to said copying sheet: 2500 parts semicarbazide,2150 :parts stannous sulfate anhydrous, 1200 parts diethano'lamine, 200parts cellulose acetate, 300 parts methanol, 1200 parts acetone and 500parts dichlorethane.

:8. A heat-sensitive copying sheet forproducing copies of printed orgraphic subject matter byexposure of said sheet, in contact with saidsubject matter, to radiant energy, said copying sheet having appliedthereto the combination of a bismuth compound and a reducing agentcapable of reacting with said bismuth compound in the presence of heatto produce metallic bismuth, the bismuth compound consisting ofapproximately 2610 parts byweight of bismuth oxychloride, which .iscombined with the following ingredients in the following approximateparts by weight for applying to said copying sheet: 2670 parts tintartrate, 2000 parts semicarbazide, 2000 parts diphenylamine, 1000 partsdi iso propanolamine, parts ethyl cellulose and 2250 parts toluene.

9. A heat-sensitive copying sheet for producing copies of printed orgraphic subject matter by exposure of said sheet, in contact with saidsubject matter, to radiant energy, said copying sheet having appliedthereto the combination of a bismuth compound and a reducing agentcapable of reacting with said'bismuth compound in the presence of heatto produce metallic bismuth, said bismuth compound consisting ofapproximately 3600 parts by weight of bismuth subsalicylate, which iscom- -.8 bined with the following ingredients in the followingapproximate parts by weight for applying to said copying sheet: 2000parts tin hydroxide, 1900 parts tri=isop ropanolamine, 250,,partspolyvinylbutyral, 2500 .parts semicarbazide and 2250 parts toluene.

10. A heat-sensitive copying sheet for producing copies of printed .orgraphic subject matter by exposure of said sheet, in contact with saidsubject matter, to radiant energy, said copying sheet having appliedthereto the combination of a bismuth compound and a reducing agentcapable of reacting with said bismuth compound in the presence ofheat'to produce metallic bismuth, said bismuth compound consisting of:approximately .2930 parts by weight of bismuth subnitrate, which 'iscombined with the following ingredients in the following approximateparts by weight for applyingto said copying sheet: 2910 partstriethylamine tin chloride, 2500 iparts semicarbazide, 1000 partsethylparatoluene sulfona'te, 200 parts cellulose nitrate and 2300'partsaceton'e.

11. A heat-sensitive copying sheet for producingicopies of printed orgraphic subject matter by exposure of said sheet, in contact withsaidsubject matter, to radiant energy, said copying sheet Ihavingapplied thereto the combination of a bismuth compound and a reducingagent capable of reacting with said bismuth compound in the presence ofheat to produce metallic bismuth, said bismuth compound being bismuthlactate, which is combined with the following ingredients ;in theapproximate proportions given tor-applying to said copyingjsheet: 36 g.bismuth lactate, 34 g. semicarbazide-tin chloride, 15 g. semicarbazide,20 g. hydrazine salicylate, 1 g. -ethyl hydroxyethyl cellulose, 50 m1.toluene and 400 ml. ligroine.

.12. A heat-sensitive copying sheet 'for producing copies of printed :orgraphic subject matter by exposure of said sheet, in contact with saidsubject matter, to radiant :energy, said copying sheet having appliedthereto the combination of "a bismuth compound and :a reducing agentcapable of reacting with said bismuth compound in the presence of heatto produce metallic bismuth, said bismuth compound being a bismuth .saltwhichiis combined with a tin derivative reducing agent inan alkalinemedium selected from the group consisting of semicarbazide, heterocyclicbases, and the aminoand ethanolamino 'deiivatives of said 'heterocyclicbas'e's.

References Cited in the file of this patent UNITED STATES PATENTS2,092,566 Wright Sept. 7, 1937 2,663,653 Zimmerman Dec. 22, 19532,663,656 Miller Dec. 22, 1953 2,740,826 Miller ...Apr. 3, 19562,749,253 Shoemaker June 5, 1956

1. A HEAT-SENSITIVE COPYING SHEET FOR PRODUCING COPIES OF PRINTED ORGRAPHIC SUBJECT MATTER BY EXPOSURE OF SAID SHEET, IN CONTACT WITH SAIDSUBJECT MATTER, TO RADIANT ENERGY, SAID COPYING SHEET HAVING APPLIEDTHERETO THE COMBINATION OF A BISMUTH COMPOUND AND A TIN DERIVATIVEREDUCING AGENT CAPABLE OF REACTING WITH SAID BISMUTH COMPOUND IN THEPRESENCE OF HEAT TO PRODUCE METALLIC BISMUTH.